Method of treating metal-coated screws



Oct. 27, 1936. R. THOMSON 2,058,841

METHOD OF TREATING METAL-COATED SCREWS Filed June 8, 1934 2 Sheets-Sheet1 IL I T 25" 5 16 iv 16 INVENTOR ROE ERT THOMSON ATTORNEYS Oct. 27,1936. R. THOMSON I 2,058,841

METHOD OF TREATING METAL-COATED SCREWS Filed June 8, 1934 2 Sheets-Sheet2 WTHH:

. INVENTOR ROBERT THOMSQN ATTORNEYS Patented Oct. 27, 1936 I METHOD OFTREATING METAL-COATED SCREWS Robert Thomson, Arlington, N. J., assignorto Dardelet Threadlock Corporation, New York, N. Y., a corporation ofDelaware Application June 8, 1934, Serial No. 729,563

14 Claims. (01. 10-1) v The present invention relates more particularlyto the galvanization of screw threaded articles. When such an article isgalvanized by the usual dipping process the distribution of thegalvanizing material over the screw-thread is quite uneven. Thegalvanizing coating is too thick at some places and too thin at others.Deposits of excess material form tears or globules on the thread andfillets in the thread groove.

deposits materially distort the .prpfile of the thread and obstruct thescrewing of the thread along a complementary thread.

Important objects of the invention are, to provide an improved method oftreating a galvanized screw threaded article to remove irregularitiesfrom the galvanizing coating and produce a smooth, uniform, accuratelygauged galvanized screw thread.

Other objects of the invention will appear hereinafter.

In the drawings, Fig. 1 is a sectional view showing the galvanizedthread of a nut being operated upon by a mandrel designed to carry outthe method;

Fig. 2 an enlarged longitudinal sectional view of a portion of the nutthread and a portion of the mandrel and showing an early stage of theoperation of the mandrel on the galvanizing coati Fig. 3 a view similarto Fig. 2 showing an ad'- vanced stage of the mandrel operation;

Fig. 4 a longitudinal sectional View of a galvanized nut thread prior totreatment to remove the irregularities on the thread coating;

Fig. 5 a view similar to Fig. 4 showing the galvanizing coating smoothedover the thread surfaces to a proper uniform thickness;

Fig. 6 a face view of an internally screw threaded die for operating onthe galvanizing 4o coating of an external screw thread to smooth thecoating over the thread surfaces and accurately shape and size thethread; v

- Fig. 7 a sectional view of said die, showing the screw thread thereofbefore it is completely shaped for its purpose;

Fig. 8 an enlarged longitudinal sectional view of the incompletelyshaped thread of the die and showing the manner in which the thread isoperated on to shape it;

Fig. 9 an enlarged longitudinal sectional view of the completely shapeddie thread;

Fig. 10 a longitudinal sectional view showing the die thread operatingon the galvanizing coating of an external screw thread; and

Fig. 11 an enlarged longitudinal sectional view These of two interfittedDardelet screw threads with galvanizing coatings that have been smoothedto accurate gauge for proper cooperation of the thrwds.

The invention is illustrated as. employed for 5 treating the galvanizingcoatings. of the wellknown Dardelet self-locking screw threads. In Fig.11, i5 designates a Dardelet externalthread, or bolt thread, and i5designates a complementary Dardelet internal thread, or nut thread. 10These threads are formed to interwedge for mutual frictionalself-locking. Each thread has a groove materially wider than its rib,and its rib has steep abutment side faces. The bolt thread i5 has athread-locking surface ll extending 15 along its root and slopingslightly, in' cross section, with reference to the axial line of thethread. Preferably the angle of slope is about six degrees' The nutthread if has a thread-locking surface it along its crest and inclinedsimilarly 20 to the surface ll of the bolt thread. In cross section theribs of both threads taper outward slightly. The nut may be freelyscrewed on the bolt, with the rib of the nut thread displaced to theleft with reference to Fig. 11 and with the 25 inclined locking surfacel8 backed away from the inclined locking surface l'l. When the nutengages an abutment however and its axial advance is arrested, furtherrotation of the nut causes axial displacement of its thread It to the 30right, with reference to Fig. 11, to force the crest surface I8 intolocking engagement with the surface H and to bring an abutment face ofthe nut thread against the opposed abutment face of the bOlt thread. 35

In the case of galvanized Dardelet threads, in order to preventobstruction of said relative axial shift of one thread on the other forlocking and unlocking the threads, the galvanizing coating should besmooth and of properly gauged thick- 40 ness over the thread surfaces.The present invention enables such a coating to be easily obtained.While the invention is of especial utility in treating galvanizedDardelet threads it may be employed very advantageously for treating 45other types of threads also. l

As indicated inFi'g. 4, the Dardelet thread surfaces of a nut N whichhas been galvanized by dipping have the zinc distributed very unevenly.The zinc coating is too thick at some 5 places and too thin at others,and globular deposits and fillets distort the profile of the thread. Tosmooth this irregular coating, reduce it to a desired uniform thicknessand accurately shape and size the thread for coaction with a comple- 55mentary thread, a mandrel I9 is provided. Said mandrel has a. reducedcylindrical entering end portion 20, a forwardly tapering portionextending throughout a length, a, a non-tapering following portion 2|extending throughout the length I), and a shank 2| squared at its outerend to fit in a driving chuck or holder. An external screw thread 22 isformed on the mandrel and extends preferably continuously throughout thetapered and non-tapered lengths or and b. Said thread has a constantpitch corresponding to that of the nut thread to be operated on. Thewidth-of the rib of the thread materially exceeds the width of thegroove so that the rib will fill the wide groove of the Dardelet nutthread H5. The helico-idal groove bottom 23 of the mandrel thread slopesin cross section similarly to the slope of the crest surface l8 of theDardelet nut thread, and the side faces 24 of the mandrel thread arecorrespondingly steep and converge slightly, to a corresponding degree.The crest surface 25 of the mandrel thread is straight in cross section.Throughout the length a it lies on a cone and throughout the length b itlies on a cylinder. The depth of the thread 22 is substantially uniformthroughout its length.

In preparation for receiving its galvanized coat-v ing the nut thread I6is cut by a tool slightly oversize and designed to cut back all of thethread surfaces to a certain degree below normal corresponding to theideal thickness of the coating. A satisfactory thickness for example isone and one-half thousandths of an inch. Therefore when the threadsurfaces have a coating ofthe calculated thickness the thread will bebrought up to normal size and proportions for cooperation with acomplementary thread. The convolutions of the mandrel thread 22 lyingwithin the length I) are accurately and uniformly profiled and gauged toconform to the ideal of the thread [6 when the latter is galvanized.Assuming therefore that the thread I6 has been accurately formed and isscrewed on said convolutions of the mandrel thread, there should be auniform space between each thread surface of the mandrel thread and theopposed basic surface of the thread l6 beneath the galvanizing coating.

The galvanizing coating is applied to the nut thread by dipping orotherwise and it may be allowed to harden. The entering end of themandrel is then passed through the galvanized nut, and relative rotationand axial advance at the proper pitch rate is caused to relativelyadvance the nut thread along the'mandrel thread. At first the leadingend portion of the mandrel thread, due to the taper, has its threadsurfaces rather widely spaced from the opposed surfaces of the nutthread, as shown in Fig. 2 axial advance continues along the taper thethread surfaces of the mandrel gradually. approach those of the nut.Consequently the excess deposits of galvanizing material are scraped,crushed and mangled to progressively increasing depth. This actioncauses considerable friction and suificient heat is thereby generated tosoften or melt the galvanizing material. The softened material isdistributed by the mandrel over the surfaces of the nut thread andcompacted thereagainst. There is thus first a crushing action whichbreaks down and mangles the excess deposits and softens thematerial ofthe coating, and a following ironing action which distributes, compactsand smoothes the softened material. By means of the non-tapered portionof the As the 'mandrel thread, included in the length b, the

material is ironed out and burnished to render the coating smooth,dense, continuous, and of the desired uniform thickness. The coatingwill then effectually protect the underlying thread surfaces fromcorrosion. The non-tapered portion of the mandrel thread serves as amaster gauge for the galvanized thread. The finished galvanized threadis shown in Fig. 5 with the coating C evenly distributed and the threadprofile cleancut and correct, for proper cooperation with acomplementary external screw thread.

For, operating on the galvanizing coating ofthe bolt thread l5 there isprovided'a die in the form of a fiat plate or block 26 having a centralbore in which a screw thread 21 is cut. The pitch of said thread isuniform, and the same as that of the bolt thread I5. The profile of thethread, however varies along the thread length. Throughout its lengththe groove bottom 28 of the thread is straight in cross section and lieson a cylinder. the length of the bore, the depth of the thread, from thegroove bottom to the highest point of the crest, is uniform and theprofile of the thread is uniform and shaped to conform accurately to anideal of the galvanized thread l5.

Its side faces 29 are steep and inclined similarly to the side faces ofthe thread 15. The crest surface 30 is inclined similarly to the rootsurface ll of the thread l5.

Along the end portions 0 and e of its length the bore of the die isoppositely flared toward the adjacent faces of the die so that the crestof the thread along said lengths c and e lies on cones and the depth ofthe thread rib increases gradually from each face inward to the lengthd. Also, the rib along each of said end lengths c and e is pared off atits opposite faces so that the rib gradually decreases in width from themedial length d to the opposite faces of the die. This cutting down ofthe rib of the thread may be performed by a tool'T with a single cuttingtooth which is screw-advanced relatively to the thread 21 and on adifferent pitch, to pare off the rib to a progressively greater depth asthe tool recedes axially from the medial portion of the thread. The toolis operated first on one side of the thread rib and then on the otherside. In Fig. 9 the die thread is shown with several taperedconvolutions within the length 0, several non-tapered convolutionswithin the length d, and one and one-half tapered convolutions withinthe length e.

In preparation for receiving its galvanizing coating the bolt thread l5also is formed by a tool or tools designed to form the thread surfacesso that they will occupy positions slightly depressed below normal to acertain degree corresponding to the ideal thickness of the coating.Therefore when the thread surfaces have a coating of the calculatedthickness the thread will attain normal size and proportions forcooperation with a complementary thread. The convolutions of the diethread lying within the length d are accurately and uniformly profiledto conform to the ideal of the thread l5 when the latter is galvanized.Assuming that the thread I5 has been accurately formed and is screwed onsaid convolutions of the die thread, there should be a uniform spacebetween each thread surface of the die thread and the opposed basicsurface of the thread l5, beneath the galvanizing coating.

The galvanizing coating is applied to the bolt Along the medial portion(1 of vanced through the die.

thread l by dipping or otherwise and it may be allowed to harden. Thebolt and die are thenaxially centered and the end of the bolt is in-'serted into the threaded end portion 0 of the bore of the die. Byrelative rotation and axial advance at the proper pitch rate the bolt,is ad- 'The tapering portion of the die thread rib penetrates the excessdeposits of galvanizing material on the bolt thread to graduallyincreasing depth as the axial advance continues, the rib filling thegroove of the bolt thread more and more. Thereby the excess deposits ofgalvanizing material are scraped, crushed and mangled. This actioncauses considerable friction and sufficient heat is thereby generated tosoften or melt the galvanizing material; The softened material isdistributed over the surfaces of the bolt thread and compacted coating Csmooth, dense, continuous and of the desired uniform thickness. Thecoating will then effectually protect the underlying thread surface fromcorrosion. The action of the nontapered portion of the die threadrenders the profile of the galvanized bolt thread clean-cut and reducesthe galvanized thread to proper dimensions for cooperation with acomplementary nut thread. Said non-tapered portion of the die threadserves as a master gauge for the galvanized thread. The taper of the diethread within the length e provides a suitable run-out for the threadand facilitates retraction of the bolt from the die with-safety tothefinished coating.

The treatment of the metallic coatings on the external and internalDardelet screw threads as described shapes and sizes the profiles of thethreads to ideal shape and dimensions so that complementary threads willhave proper working clearance for screwing and unscrewing cooperationand so that the threads will. coact properly for mutual self-locking.Any unevenness in the basic thread surfaces underlying the coating willbe corrected by the treatment of the coating. The coating is compacted,shaped, sized and burnished to produce a thread profile of highprecision accuracy over the underlying basic thread surfaces. Thetreatment of the coating. renders it hard, dense and permanent and givesit a close, fine skin texture and great wear resistance.

What I claim is:

l. The method of treating a galvanized screw-- threaded article to shapeand size the galvanized thread, comprising displacing irregularities andreducing excess thickness of the galvanizing coating by a crushingaction advanced helically along the thread and thereby softening thematerial of the coating by heat generated by friction, and fol lowingsaid crushing action with an ironing action advanced helically along thescrew thread and gauged with reference to an ideal of the thread tosmooth and compact the softened material over the surfaces of the threadand accurately shape and size the galvanized thread for cooperation witha complementary thread.

2. The method of treating a galvanized screwthreaded article to shapeand size the galvanized thread, comprising displacing irregularities ofthe galvanizing coating by a crushing action advanced helically alongthe thread and thereby softening the material of the coating by heatgenerated by friction, and following said crushing action with anironing action advanced helically along the screw thread and continuouswith the crushing action and gauged with reference to an ideal of thethread, to. smooth and compact the softened material over the surfacesof the thread and accurately shape and size the galvanized thread forcooperation with a complementary thread.

3. The method of treating a galvanized screwthreaded article to shapeand size the galvanized thread, comprising displacing irregularities .ofthe galvanizing coating by a crushing action advanced helically alongthe thread and increasing progressively and gradually in depth towardthe thread, to thereby soften the material of the coating by heatgenerated by friction, and following said crushing action with anironing action advanced helically along the screw thread and continuouswith the crushing action and gauged with reference to an ideal of thethread, to smooth and compact the softened 'material over the surfacesof the thread and accurately shape and size the galvanized thread forcooperation with a' complementary thread.

4-. The method of treating a galvanized screwthreaded article to shapeand size the galvanized thread, comprising displacing irregularities andreducing excess thickness of the coating by relatively advancing anotherscrew thread helically.

along the galvanized thread with gradual advance of the walls of .saidsecond thread transversely toward the basic walls of the galvanizedthread as said helical advance progresses, to thereby crush excessdeposits of the coating material between said walls of the threads andto heat and soften said material by heat generated by consequentfriction and to smooth the softened material over the galvanized thread.

5. The method of treating a galvanized screw thread to shape and sizethe galvanized thread, comprising displacing irregularities and reducingexcess thickness of the coating by relatively advancing helically alongthe galvanized thread a length of another screw thread tapered forgradual advance of its walls toward the basic walls of the galvanizedthread as said helical advance progresses, to crush excess deposits ofthe galvanizing material between the said walls and heat and soften saidmaterial by consequent friction and then relatively advancing helicallyalong the galvanized thread another length of thread with its walls in adefinite uniformly spaced relation to the basic walls of the galvanizedthread to smooth the softened material over said basic thread walls andaccurately govern the thickness of the coating for proper cooperation ofthe galvanized thread with a complementary thread.

6. The method of treating a galvanized internal screw thread to smooththe material of the galvanizing coating over the thread, comprisingrelatively screw-advancing along said thread a core having a screwthread to interflt said galvanized thread and shaped and gauged withrelation thereto to crush excess deposits of the galvanizing materialand heat and soften said mate'- rial by consequent friction anddistribute and galvanizing coating over the thread, comprisingrelatively screw-advancing along said thread an internal thread tointerfit said external thread and shaped and gauged with relationthereto to crush excess deposits of the galvanizing material and heatand soften said material by consequent friction and distribute andsmooth the softened material to a desired predetermined uniformthickness over the external thread.

8. The method of treating a galvanized screw thread to produce acontinuous permanent wearresisting and corrosion-preventing coating overthe thread, comprising subjecting the galvanizing coating on the threadto pressure directed and gauged to remove irregularities therefrom andto compact and smooth the coating and accurately shape and size thegalvanized thread to an ideal for proper working clearance and screwingand unscrewing cooperation with a complementary thread.

9. The method of treating a metal coated screw thread to produce acontinuous permanent wearresisting and moisture-excluding coating overthe thread, comprising subjecting the metallic coating on the thread towiping pressure advanced along the thread and progressively advanceddepthwise of the thread to remove irregularities from the coating andrender it smoothand dense, and gauging the advance of said pressuredepthwise of the coating to accurately shape and size the coated threadto an ideal for proper working clearance and screwing and unscrewingcooperation with a complementary thread.

10. The method of treating a galvanized screw threaded article toproduce a continuous permanent wear-resisting and corrosion-preventingcoating over the thread surfaces, comprising subjccting the coating onthe thread surfaces to a wiping pressure advanced along the helical pathof the thread and progressively advanced depthwise of the coating toremove irregularities from the coating and smooth and burnish it, andgauging the advance of said pressure depthwise of the coating to shapeand size the galvanized thread to an ideal for proper working clearanceand screwing and unscrewing cooperation with a complementary thread.

11. The method of producing a galvanized screw thread, comprisingforming a basic screw thread with its surfaces set back below normal adepth. corresponding to an ideal thickness of a galvanizing coating,applying a coating of galvanizing material to said thread surfaces, andtreating said coating to produce a continuous permanent wear-resistingand corrosion-preventing surface over the screw thread by subjecting thecoating to pressure directed and gauged to remove irregularities and tosmooth and compress the coating and shape and size the galvanized threadto an ideal for Working clearance and screwing and unscrewingcooperation with a complementary thread.

12. The method of producing a galvanized screw thread shaped and sizedto an ideal for working clearance and screwing and unscrewingcooperation with a complementary thread, comprising providing a basicscrew thread with its surfaces set back below normal a depthcorresponding to an ideal thickness of a galvanizing coating and with acoating of galvanizing material on said surfaces, and treating saidcoating on the basic thread surfaces by subjecting the coating topressure directed and gauged to remove irregularities from the coatingand smooth and compress it to an even continuous permanentwear-resisting and corrosion-preventing condition and shape and size thegalvanized thread to said ideal for working cooperation with acomplementary thread.

13. The method of producing a galvanized screw thread shaped and sizedto an ideal for working clearance and screwing and unscrewingcooperation with a complementary thread, comprising providing a basicthread with its surfaces set back below normal a depth corresponding toan ideal thickness for a galvanizing coating and with a coating ofgalvanizing material over said surfaces, and treating said coating onthe basic thread surfaces by subjecting the coating to wiping pressureadvanced helically along the thread and advanced progressively depthwiseof the thread to remove irregularities from the coating and smoothcompress and burnish the coating to an even continuous permanentwear-resisting and corrosion-preventing condition, and gauging theadvance of said pressure depthwise of the coating to shape and size thegalvanized thread to said ideal for cooperation with a complementarythread.

14. The method of treating a galvanized screw thread to produce acontinuous permanent wearresisting and corrosion-preventing coating overthe thread, comprising displacing irregularities and reducing excessthickness of the galvanizing coating by relatively advancing helicallyalong the galvanized thread a length of another screw thread with itsthread rib tapered helically in the direction of said advance togradually reduce

